Oxidation of aromatic lithium thiolates into sulfinate salts: an attractive entry to aryl sulfones labeled with carbon-11.

[reaction: see text] Aromatic 11C-sulfones were synthesized by S alkylation of lithium arenesulfinates, which are readily available from the corresponding thiols by an oxaziridine-mediated oxidation reaction with [11C]alkyl iodides in THF/H2O (4:1) at 150 degrees C. The radiosyntheses, including purification by HPLC, were completed in an average of 35 min from the end of the bombardment with 55-76% overall radiochemical yields (decay corrected). The described procedure extends the range of accessible labeling methods.

Highly chemoselective oxidation of dithioester enethiolates to sulfenates: application to the synthesis of ketene dithioacetal s-oxides.

Enethiolates derived from dithioesters were efficiently converted into the corresponding vinyl sulfenates by oxidation with a unique N-sulfonyloxaziridine 1a derived from pinacolone. Subsequent alkylation with alkyl halides led to ketene dithioacetal S-oxides in good to excellent yields.

New insights in the mechanism of amine catalyzed epoxidation: dual role of protonated ammonium salts as both phase transfer catalysts and activators of oxone.

Amines have previously been reported to catalyze the epoxidation of alkenes using Oxone (2KHSO(5)+KHSO(4)+K(2)SO(4)), and significant levels of asymmetric induction were observed. From screening a series of amines based on 2-substituted pyrrolidines, it has now been found that more consistent and reproducible results are achieved with the HCl salt of the amine compared to the amine itself. Up to 66% ee was achieved in epoxidation of 1-phenylcyclohexene. The chiral amine could be reisolated in >90% yield when reactions were conducted at -10 degrees C, indicating that the integrity of the amine was maintained during the oxidation process. At -10 degrees C, (S)-2-(diphenylmethyl)pyrrolidine 1 reacted with Oxone to give a mixture of ammonium salts containing the peroxymonosulfate salt 6b. The enantioselectivity obtained with this salt was compared to the amine.HCl salt catalyzed process and identical results were observed, indicating that the true oxidant was the peroxymonosulfate salt 6b. The relative rates of oxidation of cis- and trans-beta-methylstyrenes together with the rho value of a series of 1-arylcyclohexenes were determined. These studies indicated that the amine catalyzed process involved electrophilic oxidation. On the basis of these findings, a new mechanism is advanced in which the protonated amine not only acts as a PTC but also activates Oxone, through hydrogen bonding, toward electrophilic attack.

Novel approach to the synthesis of enantioenriched sulfoxides. Highly diastereoselective alkylation of sulfenate anions with 1,4-asymmetric induction.

[reaction: see text] Efficient 1,4-asymmetric induction with an enantiopure aminoalkyl group as the chiral auxiliary has been achieved in the first example of diastereoselective alkylation (up to 98:2) of a sulfenate anion, readily prepared by oxidation of the corresponding thiolate. The stereochemistry of the sulfoxide produced is the opposite of that obtained by the conventional route based on oxidation of the sulfide precursor.